The present invention relates to a system for controlling charging of a battery on a motor vehicle equipped with an internal combustion engine and using the battery for starting the engine.
Lead acid batteries are the conventional source of power for cranking internal combustion engines installed on motor vehicles. Lead acid batteries also provide auxiliary power for components installed on such vehicles for use when the vehicle engine is not operating.
Lead acid batteries operate chemically. The chemical reactions that produce current during discharge are not perfectly reversible during recharge nor are such batteries perfectly stable during periods of nonuse. A battery discharges several hundred amp-seconds during cranking of an engine. In conventional recharging systems developed for automotive applications, recharging occurs during the first few minutes after the engine begins running. Recharging is done more quickly than desirable because automobiles are often operated for short periods of time.
Lead acid batteries are constructed from closely spaced, alternating plates of sponge lead (Pb), which serve as the negative plates, and lead dioxide (PbO2), which serve as the positive plates. The plates are preferably substantially immersed in a sulfuric acid (H2SO4) water solution, which serves as an electrolyte. During discharge of a battery, lead sulfate (PbSO4) forms on both the negative and positive plates. The concentration of acid in the electrolyte decreases. As the plates become more chemically similar and the acid strength of the electrolyte falls, a battery""s voltage will begin to fall. From fully charged to fully discharged each cell loses about 0.2 volts in potential (from about 2.1 volts to 1.9 volts).
Optimally, recharging of a battery would reverse the process of discharge, strengthening the acid in the electrolyte and restoring the original chemical makeup of the plates. However, a battery recharge regimen should also keep a battery fairly fully charged for a variety of vehicle operating conditions. Battery charging systems, particularly those developed for automotive applications, must take into account average driver behavior. Many drivers do not consistently operate their vehicles for distances or times which allow the battery to be recharged at an optimal rate. Thus batteries are typically recharged quickly, resulting in polarization of the battery, overheating, and the electrolytic decomposition of the water from the battery electrolyte into hydrogen and oxygen. Vehicles also sit idle for long periods of time which promotes sulfation in the battery. These factors promote deterioration of a lead-acid battery, shortening the battery""s possible service life. In some applications a battery, which could enjoy a service life of a battery from five to eight years, gives as few as three years service.
To some extent sulfation and other factors resulting in the reduction of a lead acid battery""s charge capacity can be controlled by avoiding overcharging, or by avoiding overheating of the battery stemming from excessively fast recharging. The development of a vehicle electrical system applicable to certain classes of vehicles which extends battery life is desirable.
To insure that batteries are fully charged, conventional 12 volt vehicle electrical systems operate at an over voltage, typically 14.3 volts. Such high voltages tend to shorten service lives for accessory components, particularly lamps. It is further desirable to provide a vehicle electrical system which does not shorten the service lives of other vehicle accessory components.
The present invention is directed to an electrical system that satisfies the need for battery charging on a vehicle, promoting a longer service life for the battery and for accessory components installed on the vehicle. The electrical system comprises a lead acid battery having two terminals. A current sensor is coupled to one terminal of the battery for measuring current sourced from and delivered to the battery. A temperature sensor is positioned proximate to the battery for measuring battery temperature. A controllable voltage regulator is provided which is responsive to a control signal for adjustment of voltage on an output terminal of the regulator which supplies the battery charging current to the battery. The controllable voltage regulator has input and output terminals and is connected by the output terminal to one terminal of the battery for supplying charging current delivered to the battery. An electrical system controller responsive to the measured current sourced from the battery and the measured battery temperature generates the control signal to be applied to the controllable voltage regulator. Energization of the components is provided by an alternator connected to the input of the controllable voltage regulator. The system further includes a lighting system or low voltage circuit and a low voltage regulator connected between the alternator and the lighting system circuit. Voltage on an engine control or high voltage circuit is regulated by an engine control circuit or high voltage regulator connected between the alternator and the engine control circuit.
Additional effects, features and advantages will be apparent in the written description that follows.